Cyclic AMP-specific phosphodiesterase inhibitors

ABSTRACT

Novel compounds that are potent and selective inhibitors of PDE4, as well as methods of making the same, are disclosed. Use of the compounds in the treatment of inflammatory diseases and other diseases involving elevated levels of cytokines, as well as central nervous system (CNS) disorders, also is disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 09/716,024,filed Nov. 17, 2000, which claims the benefit of provisional applicationSerial No. 60/171,955, filed Dec. 23, 1999.

FIELD OF INVENTION

The present invention relates to a series of compounds that are potentand selective inhibitors of cyclic adenosine 3′,5′-monophosphatespecific phosphodiesterase (cAMP specific PDE). In particular, thepresent invention relates to a series of novel oxime and hydrazonecompounds that are useful for inhlbiting the function of cAMP specificPDE, in particular, PDE4, as well as methods of making the same,pharmaceutical compositions containing the same, and their use astherapeutic agents, for example, in treating inflammatory diseases andother diseases involving elevated levels of cytokines andproinflammatory mediators.

BACKGROUND OF THE INVENTION

Chronic inflammation is a multi-factorial disease complicationcharacterized by activation of multiple types of inflammatory cells,particularly cells of lymphoid lineage (including T lymphocytes) andmyeloid lineage (including granulocytes, macrophages, and monocytes).Proinflammatory mediators, including cytokines, such as tumor necrosisfactor (TNF) and interleukin-1 (IL-1), are produced by these activatedcells. Accordingly, an agent that suppresses the activation of thesecells, or their production of proinflammatory cytokines, would be usefulin the therapeutic treatment of inflammatory diseases and other diseasesinvolving elevated levels of cytokines.

Cyclic adenosine monophosphate (cAMP) is a second messenger thatmediates the biologic responses of cells to a wide range ofextracellular stimuli. When the appropriate agonist binds to specificcell surface receptors, adenylate cyclase is activated to convertadenosine triphosphate (ATP) to cAMP. It is theorized that the agonistinduced actions of cAMP within the cell are mediated pre-dominately bythe action of cAMP-dependent protein kinases. The intracellular actionsof cAMP are terminated by either a transport of the nucleotide to theoutside of the cell, or by enzymatic cleavage by cyclic nucleotidephosphodiesterases (PDEs), which hydrolyze the 3′-phosphodiester bond toform 5′-adenosine monophosphate (5′-AMP). 5′-AMP is an inactivemetabolite. The structures of cAMP and 5′-AMP are illustrated below.

Elevated levels of cAMP in human myeloid and lymphoid lineage cells areassociated with the suppression of cell activation. The intracellularenzyme family of PDES, therefore, regulates the level of cAMP in cells.PDE4 is a predominant PDE isotype in these cells, and is a majorcontributor to cAMP degradation. Accordingly, the inhibition of PDEfunction would prevent the conversion of cAMP to the inactive metabolite5′-AMP and, consequently, maintain higher cAMP levels, and, accordingly,suppress cell activation (see Beavo et al., “Cyclic NucleotidePhosphodiesterases: Structure, Regulation and Drug Action,” Wiley andSons, Chichester, pp. 3-14, (1990)); Torphy et al., Drug News andPerspectives, 6, pp. 203-214 (1993); Giembycz et al., Clin. Exp.Allergy, 22, pp. 337-344 (1992)).

In particular, PDE4 inhibitors, such as rolipram, have been shown toinhibit production of TNFα and partially inhibit IL-1β release bymonocytes (see Semmler et al., Int. J. Immunopharmacol., 15, pp.409-413, (1993); Molnar-Kimber et al., Mediators of Inflammation, 1, pp.411-417, (1992)). PDE4 inhibitors also have been shown to inhibit theproduction of superoxide radicals from human polymorphonuclearleukocytes (see Verghese et al., J. Mol. Cell. Cardiol., 21 (Suppl. 2),S61 (1989); Nielson et al., J. Allergy Immunol., 86, pp. 801-808,(1990)); to inhibit the release of vasoactive amines and prostanoidsfrom human basophils (see Peachell et al., J. Immunol., 148, pp.2503-2510, (1992)); to inhibit respiratory bursts in eosinophils (seeDent et al., J. Pharmacol., 103, pp. 1339-1346, (1991)); and to inhibitthe activation of human T-lymphocytes (see Robicsek et al., Biochem.Pharmacol., 42, pp. 869-877, (1991)).

Inflammatory cell activation and excessive or unregulated cytokine(e.g., TNFα and IL-1β) production are implicated in allergic,autoimmune, and inflammatory diseases and disorders, such as rheumatoidarthritis, osteoarthritis, gouty arthritis, spondylitis, thyroidassociated ophthalmopathy, Behcet's disease, sepsis, septic shock,endotoxic shock, gram negative sepsis, gram positive sepsis, toxic shocksyndrome, asthma, chronic bronchitis, adult respiratory distresssyndrome, chronic pulmonary inflammatory disease, such as chronicobstructive pulmonary disease, silicosis, pulmonary sarcoidosis,reperfusion injury of the myocardium, brain, and extremities, fibrosis,cystic fibrosis, keloid formation, scar formation, atherosclerosis,transplant rejection disorders, such as graft vs. host reaction andallograft rejection, chronic glomerulonephritis, lupus, inflammatorybowel disease, such as Crohn's disease and ulcerative colitis,proliferative lymphocyte diseases, such as leukemia, and inflammatorydermatoses, such as atopic dermatitis, psoriasis, and urticaria.

Other conditions characterized by elevated cytokine levels include braininjury due to moderate trauma (see Dhillon et al., J. Neurotrauma, 12,pp. 1035-1043 (1995); Suttorp et al., J. Clin. Invest., 91, pp.1421-1428 (1993)), cardiomyopathies, such as congestive heart failure(see Bristow et al., Circulation, 97, pp. 1340-1341 (1998)), cachexia,cachexia secondary to infection or malignancy, cachexia secondary toacquired immune deficiency syndrome (AIDS), ARC (AIDS related complex),fever myalgias due to infection, cerebral malaria, osteoporosis and boneresorption diseases, keloid formation, scar tissue formation, andpyrexia.

In particular, TNFα has been identified as having a role with respect tohuman acquired immune deficiency syndrome (AIDS). AIDS results from theinfection of T-lymphocytes with Human Immunodeficiency Virus (HIV).Although HIV also infects and is maintained in myeloid lineage cells,TNF has been shown to upregulate HIV infection in T-lymphocytic andmonocytic cells (see Poli et al., Proc. Natl. Acad. Sci. USA, 87, pp.782-785, (1990)).

Several properties of TNFα, such as stimulation of collagenases,stimulation of angiogenesis in vivo, stimulation of bone resorption, andan ability to increase the adherence of tumor cells to endothelium, areconsistent with a role for TNF in the development and metastatic spreadof cancer in the host. TNFα recently has been directly implicated in thepromotion of growth and metastasis of tumor cells (see Orosz et al., J.Exp. Med., 177, pp. 1391-1398, (1993)).

PDE4 has a wide tissue distribution. There are at least four genes forPDE4 of which multiple transcripts from any given gene can yield severaldifferent proteins that share identical catalytic sites. The amino acididentity between the four possible catalytic sites is greater than 85%.Their shared sensitivity to inhibitors and their kinetic similarityreflect the functional aspect of this level of amino acid identity. Itis theorized that the role of these alternatively expressed PDE4proteins allows a mechanism by which a cell can differentially localizethese enzymes intracellularly and/or regulate the catalytic efficiencyvia post translational modification. Any given cell type that expressesthe PDE4 enzyme typically expresses more than one of the four possiblegenes encoding these proteins.

Investigators have shown considerable interest in the use of PDE4inhibitors as anti-inflammatory agents. Early evidence indicates thatPDE4 inhibition has beneficial effects on a variety of inflammatorycells such as monocytes, macrophages, T-cells of the Th-1 lineage, andgranulocytes. The synthesis and/or release of many proinflammatorymediators, such as cytokines, lipid mediators, superoxide, and biogenicamines, such as histamine, have been attenuated in these cells by theaction of PDE4 inhibitors. The PDE4 inhibitors also affect othercellular functions including T-cell proliferation, granulocytetransmigration in response to chemotoxic substances, and integrity ofendothelial cell junctions within the vasculature.

The design, synthesis, and screening of various PDE4 inhibitors havebeen reported. Methylxanthines, such as caffeine and theophylline, werethe first PDE inhibitors discovered, but these compounds arenonselective with respect to which PDE is inhibited. The drug rolipram,an antidepressant agent, was one of the first reported specific PDE4inhibitors. Rolipram, having the following structural formula, has areported 50% Inhibitory Concentration (IC₅₀) of about 200 nM (nanomolar)with respect to inhibiting recombinant human PDE4.

Investigators have continued to search for PDE4 inhibitors that are moreselective with respect to inhibiting PDE4, that have a lower IC₅₀ thanrolipram, and that avoid the undesirable central nervous system (CNS)side effects, such as retching, vomiting, and sedation, associated withthe administration of rolipram. One class of compounds is disclosed inFeldman et al. U.S. Pat. No. 5,665,754. The compounds disclosed thereinare substituted pyrrolidines having a structure similar to rolipram. Oneparticular compound, having structural formula (I), has an IC₅₀ withrespect to human recombinant PDE4 of about 2 nM. Inasmuch as a favorableseparation of emetic side effect from efficacy was observed, thesecompounds did not exhibit a reduction in undesirable CNS effects.

In addition, several companies are now undertaking clinical trials ofother PDE4 inhibitors. However, problems relating to efficacy andadverse side effects, such as emesis and central nervous systemdisturbances, remain unsolved.

Accordingly, compounds that selectively inhibit PDE4, and that reduce oreliminate the adverse CNS side effects associated with prior PDE4inhibitors, would be useful in the treatment of allergic andinflammatory diseases, and other diseases associated with excessive orunregulated production of cytokines, such as TNF. In addition, selectivePDE4 inhibitors would be useful in the treatment of diseases that areassociated with elevated cAMP levels or PDE4 function in a particulartarget tissue.

SUMMARY OF THE INVENTION

The present invention is directed to potent and selective PDE4inhibitors useful in treatment of diseases and conditions whereinhibition of PDE4 activity is considered beneficial. The present PDE4inhibitors unexpectedly reduce or eliminate the adverse CNS side effectsassociated with prior PDE4 inhibitors.

In particular, the present invention is directed to compounds having thestructural formula (II):

wherein Y is OR⁵ or NR⁵R⁶;

R¹ is lower alkyl, bridged alkyl (e.g., norbornyl), aralkyl (e.g.,indanyl), cycloalkyl, a 5- or 6-membered saturated heterocycle (e.g.,3-tetrahydrofuryl), C₁₋₃alkylenecycloalkyl (e.g., cyclopentylmethyl),aryl- or heteroaryl-substituted propargyl (e.g., —CH₂C≡C—C₆H₅), aryl- orheteroarylsubstituted allyl (e.g., —CH₂CH═CH—C₆H₅), or halocycloalkyl(e.g., fluorocyclopentyl);

R² is hydrogen, methyl, or halo-substituted methyl, e.g., CHF₂;

R³ is C(═O)OR⁷, C(═O)R⁷, C(═NH)NR⁸R⁹, C(═O)—NR⁸ R⁹, aryl, or heteroaryl;

R⁴ is hydrogen, lower alkyl, haloalkyl, cycloalkyl, or aryl;

R⁵ and R⁶, independently, are hydrogen, lower alkyl, haloalkyl,cycloalkyl, aryl, heteroaryl, or alkaryl, or R³ and R⁶ are takentogether form a 5-membered or 6-membered ring;

R⁷ is branched or unbranched lower alkyl or aryl, or R⁷ can beoptionally substituted with one or more of OR⁸, NR⁸R⁹, or SR⁸;

R⁸ and R⁹, same or different, are selected from the group consisting ofhydrogen, lower alkyl, cycloalkyl, aryl, heteroaryl, and aralkyl, or R⁸and R⁹ are taken together form a 4-membered to 7-membered ring;

R¹⁰ is hydrogen, alkyl, haloalkyl, cycloalkyl, aryl, C(═O)alkyl,C(═O)cycloalkyl, c(═O)aryl, C(═O)Oalkyl, C(═O)Ocycloalkyl, C(═O)aryl,CH₂OH, CH₂Oalkyl, CHO, CN, NO₂, or SO₂R¹¹; and

R¹¹ is alkyl, cycloalkyl, trifluoromethyl, aryl, aralkyl, or NR⁸R⁹.

The present invention also is directed to pharmaceutical compositionscontaining one or more of the compounds of structural formula (II), touse of the compounds and compositions containing the compounds in thetreatment of a disease or disorder, and to methods of preparingcompounds and intermediates involved in the synthesis of the compoundsof structural formula (II).

The present invention also is directed to methods of treating a mammalhaving a condition where inhibition of PDE4 provides a benefit,modulating cAMP levels in a mammal, reducing TNFα levels in a mammal,suppressing inflammatory cell activation in a mammal, and inhibitingPDE4 function in a mammal by administering therapeutically effectiveamounts of a compound of structural formula (II), or a compositioncontaining a composition of structural formula (II) to the mammal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed to compounds having the structuralformula (II):

wherein Y is OR⁵ or NR⁵R⁶;

R¹ is lower alkyl, bridged alkyl (e.g., norbornyl), aralkyl (e.g.,indanvl), cycloalkyl, a 5- or 6-membered saturated heterocycle (e.g.,3-tetrahydrofuryl), C₁₋₃alkylenecycloalkyl (e.g., cyclopentylmethyl),aryl- or heteroaryl-substituted propargyl (i.e., —CH₂C≡C—C₆H₅), aryl- orheteroaryl-substituted allyl (e.g., —CH₂CH═CH—C₆H₅), or halo-cycloalkyl(e.g., fluorocyclopentyl);

R² is hydrogen, methyl, or halo-substituted methyl, e.g., CHF₂;

R³ is C(═O)OR⁷, C(═O)R⁷, C(═NH)NR⁸R⁹, C(═O)—NR⁸R⁹, aryl, or heteroaryl;

R⁴ is hydrogen, lower alkyl, haloalkyl, cycloalkyl, or aryl;

R⁵ and R⁶, independently, are hydrogen, lower alkyl, haloalkyl,cycloalkyl, aryl, heteroaryl, or alkaryl, or R⁵ and R⁶ are takentogether form a 5-membered or 6-membered ring;

R⁷ is branched or unbranched lower alkyl or aryl, or R⁷ can beoptionally substituted with one or more of OR⁸, NR⁸R⁹, or SR⁸; and

R⁸ and R⁹, same or different, are selected from the group consisting ofhydrogen, lower alkyl, cycloalkyl, aryl, heteroaryl, and aralkyl, or R⁸and R⁹ are taken together form a 4-membered to 7-membered ring;

R¹⁰ is hydrogen, alkyl, haloalkyl, cycloalkyl, aryl, C(═O)alkyl,C(═O)cycloalkyl, C(═O)aryl, C(═O)Oalkyl, C(═O)Ocycloalkyl, C(═O)aryl,CH₂OH, CH₂Oalkyl, CHO, CN, NO₂, or SO₂R¹¹; and

R¹¹ is alkyl, cycloalkyl, trifluoromethyl, aryl, aralkyl, or NR⁸R⁹.

As used herein, the term “alkyl,” alone or in combination, is defined toinclude straight chain and branched chain saturated hydrocarbon groupscontaining one to 16 carbon atoms. The term “lower alkyl” is definedherein as an alkyl group having one through six carbon atoms (C₁-C₆).Examples of lower alkyl groups include, but are not limited to, methyl,ethyl, n-propyl, isopropyl, isobutyl, n-butyl, neopentyl, n-hexyl, andthe like. The term “alkynyl” refers to an unsaturated alkyl group thatcontains a carbon-carbon triple bond.

The term “bridged alkyl” is defined herein as a C₆-C₁₆ bicyclic orpolycyclic hydrocarbon group, for example, norboryl, adamantyl,bicyclo[2.2.2]octyl, bicyclo[2.2.1]heptyl, bicyclo[3.2.1]octyl, ordecahydronaphthyl.

The term “cycloalkyl” is defined herein to include cyclic C₃-C₇hydrocarbon groups. Examples of cycloalkyl groups include, but are notlimited to, cyclopropyl, cyclobutyl, cyclohexyl, and cyclopentyl.

The term “alkylene” refers to an alkyl group having a substituent. Forexample, the term “C₁₋₃alkylenecycloalkyl” refers to an alkyl groupcontaining one to three carbon atoms, and substituted with a cycloalkylgroup.

The term “haloalkyl” is defined herein as an alkyl group substitutedwith one or more halo substituents, either fluro, chloro, bromo, iodo,or combinations thereof. Similarly, “halocycloalkyl” is defined as acycloalkyl group having one or more halo substituents.

The term “aryl,” alone or in combination, is defined herein as amonocyclic or polycyclic aromatic group, preferably a monocyclic orbicyclic aromatic group, e.g., phenyl or naphthyl, that can beunsubstituted or substituted, for example, with one or more, and inparticular one to three, substituents selected from halo, alkyl,hydroxy, hydroxyalkyl, alkoxy, alkoxyalkyl, haloalkyl, nitro, amino,alkylamino, acylamino, alkylthio, alkylsulfinyl, and alkylsulfonyl.Exemplary aryl groups include phenyl, naphthyl, tetrahydronaphthyl,2-chlorophenyl, 3-chlorophenyl, 4-chlorophenyl, 2-methylphenyl,4-methoxyphenyl, 3-trifluoromethylphenyl, 4-nitrophenyl, and the like.

The term “heteroaryl” is defined herein as a monocyclic or bicyclic ringsystem containing one or two aromatic rings and containing at least onenitrogen, oxygen, or sulfur atom in an aromatic ring, and which can beunsubstituted or substituted, for example, with one or more, and inparticular one to three, substituents, like halo, alkyl, hydroxy,hydroxyalkyl, alkoxy, alkoxyalkyl, haloalkyl, nitro, amino, alkylamino,acylamino, alkylthio, alkylsulfinyl, and alkylsulfonyl. Examples ofheteroaryl groups include thienyl, furyl, pyridyl, oxazolyl, quinolyl,isoquinolyl, indolyl, triazolyl, isothiazolyl, isoxazolyl, imidizolyl,benzothiazolyl, pyrazinyl, pyrimidinyl, thiazolyl, and thiadiazolyl.

The term “aralkyl” is defined herein as a previously defined alkylgroup, wherein one of the hydrogen atoms is replaced by an aryl group asdefined herein, for example, a phenyl group optionally having one ormore substituents, for example, halo, alkyl, alkoxy, and the like. Anexample of an aralkyl group is a benzyl group.

The term “alkaryl” is defined herein as a previously defined aryl group,wherein one of the hydrogen atoms is replaced by an alkyl, cycloalkyl,haloalkyl, or halocycloalkyl group.

The terms “heteroaralkyl” and “heteroalkaryl” are defined similarly asthe term “aralkyl”and “alkaryl,” however, the aryl group is replaced bya heteroaryl group as previously defined.

The term “heterocycle” is defined as a 5- or 6-membered nonaromatic ringhaving one or more heteroatoms selected from oxygen, nitrogen, andsulfur present in the ring. Nonlimiting examples includetetrahydrofuran, piperdine, piperazine, sulfolane, morpholine,tetrahydropyran, dioxane, and the like.

The term “halogen” or “halo” is defined herein to include fluorine,chlorine, bromine, and iodine.

The term “alkoxy” is defined as —OR, wherein R is alkyl.

The term “alkoxyalkyl” is defined as an alkoxy group appended to analkyl group. The terms “aryloxyalkyl” and “aralkoxyalkyl” are similarlydefined as an aryloxy or aralkoxy group appended to an alkyl group.

The term “hydroxy” is defined as —OH.

The term “hydroxyalkyl” is defined as a hydroxy group appended to analkyl group.

The term “amino” is defined as —NH₂.

The term “alkylamino” is defined as —NR₂ wherein at least one R is alkyland the second R is alkyl or hydrogen.

The term “acylamino” is defined as RC(═O)N, wherein R is alkyl or aryl.

The term “nitro” is defined as —NO₂.

The term “alkylthio” is defined as —SR, where R is alkyl.

The term “alkylsulfinyl” is defined as R—SO₂, where R is alkyl.

The term “alkylsulfonyl” is defined as R—SO₃, where R is alkyl.

In preferred embodiments, R⁷ is methyl, R² is methyl or difluoromethyl,R⁴ is selected from the group consisting of hydrogen, methyl,trifluoromethyl, cyclopropyl, acetyl, ethynyl, benzyl, and phenyl, andR⁵ and R⁶ are selected the group consisting of hydrogen and methyl. R¹is selected from the group consisting of

R³ is selected from the group consisting of

In most preferred embodiments, R¹ is selected from the group consistingof cyclopentyl, tetrahydrofuryl, indanyl, norbornyl, phenethyl, andphenylbutyl; R² is selected from the group consisting of methyl anddifluoromethyl; R³ is selected from the group consisting of CO₂CH₃,C(═O)CH₂OH, C(═O)CH(CH₃)—OH, C(═O)C(CH₃)₂OH, and

R⁴ is hydrogen or methyl; R⁵ and R⁶, independently, are hydrogen ormethyl, or R⁵ and R⁶ together form a 5-membered or 6-membered ring; andR¹⁰ is hydrogen.

The present invention includes all possible stereoisomers and geometricisomers of compounds of structural formula (II), and includes not onlyracemic compounds but also the optically active isomers as well. When acompound of structural formula (II) is desired as a single enantiomer,it can be obtained either by resolution of the final product or bystereospecific synthesis from either isomerically pure starting materialor use of a chiral auxiliary reagent, for example, see Z. Ma et al.,Tetrahedron: Asymmetry, 8(6), pages 883-888 (1997). Resolution of thefinal product, an intermediate, or a starting material can be achievedby any suitable method known in the art. Additionally, in situationswhere tautomers of the compounds of structural formula (II) arepossible, the present invention is intended to include all tautomericforms of the compounds. As demonstrated hereafter, specificstereoisomers exhibit an exceptional ability to inhibit PDE4 withoutmanifesting the adverse CNS side effects typically associated with PDE4inhibitors.

In particular, it is generally accepted that biological systems canexhibit very sensitive activities with respect to the absolutestereochemical nature of compounds. (See, E. J. Ariens, MedicinalResearch Reviews, 6:451-466 (1986); E. J. Ariens, Medicinal ResearchReviews, 7:367-387 (1987); K. W. Fowler, Handbook of Stereoisomers:Therapeutic Drugs, CRC Press, edited by Donald P. Smith, pp. 35-63(1989); and S. C. Stinson, Chemical and Engineering News, 75:38-70(1997).)

For example, rolipram is a stereospecific PDE4 inhibitor that containsone chiral center. The (−)-enantiomer of rolipram has a higherpharmacological potency than the (+)-enantiomer, which could be relatedto its potential antidepressant action. Schultz et al.,Naunyn-Schmiedeberg's Arch Pharmacol, 333:23-30 (1986). Furthermore, themetabolism of rolipram appears stereospecific with the (+)-enantiomerexhibiting a faster clearance rate than the (−)-enantiomer. Krause etal., Xenobiotica, 18:561-571 (1988). Finally, a recent observationindicated that the (−)-enantiomer of rolipram (R-rolipram) is aboutten-fold more emetic than the (+)-enantiomer (S-rolipram). A. Robichaudet al., Neuropharmacology, 38:289-297 (1999). This observation is noteasily reconciled with differences in test animal disposition torolipram isomers and the ability of rolipram to inhibit the PDE4 enzyme.The compounds of the present inventor can have three chiral centers. Asshown below, compounds of a specific stereochemical orientation exhibitsimilar PDE4 inhibitory activity and pharmacological activity, butaltered CNS toxicity and emetic potential.

Accordingly, preferred compounds of the present invention have thestructural formula (III):

The compounds of structural formula (III) are potent and selective PDE4inhibitors, and do not manifest the adverse CNS effects and emeticpotential demonstrated by stereoisomers of a compound of structuralformula (III).

Compounds of structural formula (II) which contain acidic moieties canform pharmaceutically acceptable salts with suitable cations. Suitablepharmaceutically acceptable cations include alkali metal (e.g., sodiumor potassium) and alkaline earth metal (e.g., calcium or magnesium)cations. The pharmaceutically acceptable salts of the compounds ofstructural formula (II), which contain a basic center, are acid additionsalts formed with pharmaceutically acceptable acids. Examples includethe hydrochloride, hydrobromide, sulfate or bisulfate, phosphate orhydrogen phosphate, acetate, benzoate, succinate, fumarate, maleate,lactate, citrate, tartrate, gluconate, methanesulfonate,benzenesulphonate, and p-toluenesulphonate salts. In light of theforegoing, any reference to compounds of the present invention appearingherein is intended to include compounds of structural formula (II), aswell as pharmaceutically acceptable salts and solvates thereof.

The compounds of the present invention can be therapeuticallyadministered as the neat chemical, but it is preferable to administercompounds of structural formula (II) as a pharmaceutical composition orformulation. Accordingly, the present invention further provides forpharmaceutical formulations comprising a compound of structural formula(II), together with one or more pharmaceutically acceptable carriersand, optionally, other therapeutic and/or prophylactic ingredients. Thecarriers are “acceptable” in the sense of being compatible with theother ingredients of the formulation and not deleterious to therecipient thereof.

In particular, a selective PDE4 inhibitor of the present invention isuseful alone or in combination with a second antiinflammatorytherapeutic agent, for example, a therapeutic agent targeting TNFα, suchas ENBREL® or REMICADE®, which have utility in treating rheumatoidarthritis. Likewise, therapeutic utility of IL-1 antagonism has alsobeen shown in animal models for rheumatoid arthritis. Thus, it isenvisioned that IL-1 antagonism, in combination wihh PDE4 inhibition,which attenuates TNFα, would be efficacious.

The present PDE4 inhibitors are useful in the treatment of a variety ofallergic, autoimmune, and inflammatory diseases.

The term “treatment” includes preventing, lowering, stopping, orreversing the progression of severity of the condition or symptoms beingtreated. As such, the term “treatment” includes both medical therapeuticand/or prophylactic administration, as appropriate.

In particular, inflammation is a localized, protective response elicitedby injury or destruction of tissues, which serves to destroy, dilute orwall off (i.e., sequester) both the injurious agent and the injuredtissue. The term “inflammatory disease,” as used herein, means anydisease in which an excessive or unregulated inflammatory response leadsto excessive inflammatory symptoms, host tissue damage, or loss oftissue function. Additionally, the term “autoimmune disease,” as usedherein, means any group of disorders in which tissue injury isassociated with humoral or cell-mediated responses to the body's ownconstituents. The term “allergic disease,” as used herein, means anysymptoms, tissue damage, or loss of tissue function resulting fromallergy. The term “arthritic disease,” as used herein, means any of alarge family of diseases that are characterized by inflammatory lesionsof the joints attributable to a variety of etiologies. The term“dermatitis,” as used herein, means any of a large family of diseases ofthe skin that are characterized by inflammation of the skin attributableto a variety of etiologies. The term “transplant rejection,” as usedherein, means any immune reaction directed against grafted tissue(including organ and cell (e.g., bone marrow)), characterized by a lossof function of the grafted and surrounding tissues, pain, swelling,leukocytosis and thrombocytopenia.

The present invention also provides a method of modulating cAMP levelsin a mammal, as well as a method of treating diseases characterized byelevated cytokine levels.

The term “cytokine,” as used herein, means any secreted polypeptide thataffects the functions of other cells, and that modulates interactionsbetween cells in the immune or inflammatory response. Cytokines include,but are not limited to monokines, lymphokines, and chemokines regardlessof which cells produce them. For instance, a monokine is generallyreferred to as being produced and secreted by a monocyte, however, manyother cells produce monokines, such as natural killer cells,fibroblasts, basophils, neutrophils, endothelial cells, brainastrocytes, bone marrow stromal cells, epidermal keratinocytes, andB-lymphocytes. Lymphokines are generally referred to as being producedby Examples of cytokines include, but are not limited to, interleukin-1(IL-1), interleukin-6 (IL-6), Tumor Necrosis Factor alpha (TNFα), andTumor Necrosis Factor beta (TNFβ).

The present invention further provides a method of reducing TNF levelsin a mammal, which comprises administering an effective amount of acompound of structural formula (II) to the mammal. The term “reducingTNF levels,” as used herein, means either:

a) decreasing excessive in vivo TNF levels in a mammal to normal levelsor below normal levels by inhibition of the in vivo release of TNF byall cells, including but not limited to monocytes or macrophages; or

b) inducing a down-regulation, at the translational or transcriptionlevel, of excessive in vivo TNF levels in a mammal to normal levels orbelow normal levels; or

c) inducing a down-regulation, by inhibition of the direct synthesis ofTNF as a postranslational event.

Moreover, the compounds of the present invention are useful insuppressing inflammatory cell activation. The term “inflammatory cellactivation,” as used herein, means the induction by a stimulus(including, but not limited to, cytokines, antigens or auto-antibodies)of a proliferative cellular response, the production of solublemediators (including but not limited to cytokines, oxygen radicals,enzymes, prostanoids, or vasoactive amines), or cell surface expressionof new or increased numbers of mediators (including, but not limited to,major histocompatability antigens or cell adhesion molecules) ininflammatory cells (including but not limited to monocytes, macrophages,T lymphocytes, B lymphocytes, granulocytes, polymorphonuclearleukocytes, mast cells, basophils, eosinophils, dendritic cells, andendothelial cells). It will be appreciated by persons skilled in the artthat the activation of one or a combination of these phenotypes in thesecells can contribute to the initiation, perpetuation, or exacerbation ofan inflammatory condition.

The compounds of the present invention also are useful in causing airwaysmooth muscle relaxation, bronchodilation, and prevention ofbronchoconstriction.

The compounds of the present invention, therefore, are useful intreating such diseases as arthritic diseases (such as rheumatoidarthritis), osteoarthritis, gouty arthritis, spondylitis,thyroid-associated ophthalmopathy, Behcet disease, sepsis, septic shock,endotoxic shock, gram negative sepsis, gram positive sepsis, toxic shocksyndrome, asthma, chronic bronchitis, allergic rhinitis, allergicconjunctivitis, vernal conjunctivitis, eosinophilic granuloma, adult(acute) respiratory distress syndrome (ARDS), chronic pulmonaryinflammatory disease (such as chronic obstructive pulmonary disease),silicosis, pulmonary sarcoidosis, reperfusion injury of the myocardium,brain or extremities, brain or spinal cord injury due to minor trauma,fibrosis including cystic fibrosis, keloid formation, scar tissueformation, atherosclerosis, autoimmune diseases, such as systemic lupuserythematosus (SLE) and transplant rejection disorders (e.g., graft vs.host (GvH) reaction and allograft rejection), chronicglomerulonephritis, inflammatory bowel diseases, such as Crohn's diseaseand ulcerative colitis, proliferative lymphocytic diseases, such asleukemias (e.g. chronic lymphocytic leukemia; CLL) (see Mentz et al.,Blood 88, pp. 2172-2182 (1996)), and inflammatory dermatoses such asatopic dermatitis, psoriasis, or urticaria.

Other examples of such diseases or related conditions includecardiomyopathies, such as congestive heart failure, pyrexia, cachexia,cachexia secondary to infection or malignancy, cachexia secondary toacquired immune deficiency syndrome (AIDS), ARC (AIDS-related complex),cerebral malaria, osteoporosis and bone resorption diseases, and feverand myalgias due to infection. In addition, the compounds of the presentinvention are useful in the treatment of diabetes insipidus and centralnervous system disorders, such as depression and multi-infarct dementia.

Compounds of the present invention also have utility outside of thattypically known as therapeutic. For example, the present compounds canfunction as organ transplant preservatives (see Pinsky et al., J. Clin.Invest., 92, pp. 2994-3002 (1993)) as well.

Selective PDE4 inhibitors also can be useful in the treatment oferectile dysfunction, especially vasculogenic impotence (Doherty, Jr. etal. U.S. Pat. No. 6,127,363), diabetes insipidus (Kidney Int., 37, p.362, (1990); Kidney Int., 35, p. 494, (1989)), and central nervoussystem disorders, such as multiinfarct dementia (Nicholson,Psychopharmacology, 101, p. 147 (1990)), depression (Eckman et al.,Curr. Ther. Res., 43, p. 291 (1988)), anxiety and stress responses(Neuropharmacology, 38, p. 1831 (1991)), cerebral ischemia (Eur. J.Pharmacol., 272, p. 107 (1995)), tardive dyskinesia (J. Clin.Pharmocol., 16, p. 304 (1976)), Parkinson's disease (see Neurology, 25,p. 722 (1975); Clin. Exp. Pharmacol, Physiol., 26, p. 421 (1999)), andpremenstrual syndrome. With respect to depression, PDE4-selectiveinhibitors show efficacy in a variety of animal models of depressionsuch as the “behavioral despair” or Porsolt tests (Eur. J. Pharmacol.,47, p. 379 (1978); Eur. J. Pharmacol., 57, p. 431 (1979);Antidepressants: neurochemical, behavioral and clinical prospectives,Enna, Malick, and Richelson, eds., Raven Press, p. 121 (1981)), and the“tail suspension test” (Psychopharmacology, 85, p. 367 (1985)). Recentresearch findings show that chronic in vivo treatment by a variety ofantidepressants increase the brain-derived expression of PDE4 (J.Neuroscience, 19, p. 610 (1999)). Therefore, a selective PDE4 inhibitorcan be used alone or in conjunction with a second therapeutic agent in atreatment for the four major classes of antidepressants:electroconvulsive procedures, monoamine oxidase inhibitors, andselective reuptake inhibitors of serotonin or norepinephrine. SelectivePDE4 inhibitors also can be useful in applications that modulatebronchodilatory activity via direct action on bronchial smooth musclecells for the treatment of asthma.

Compounds and pharmaceutical compositions suitable for use in thepresent invention include those wherein the active ingredient isadministered to a mammal in an effective amount to achieve its intendedpurpose. More specifically, a “therapeutically effective amount” meansan amount effective to prevent development of, or to alleviate theexisting symptoms of, the subject being treated. Determination of theeffective amounts is well within the capability of those skilled in theart, especially in light of the detailed disclosure provided herein.

The term “mammal” as used herein includes males and females, andencompasses humans, domestic animals (e.g., cats, dogs), livestock(e.g., cattle, horses, swine), and wildlife (e.g., primates, large cats,zoo specimens).

A “therapeutically effective dose” refers to that amount of the compoundthat results in achieving the desired effect. Toxicity and therapeuticefficacy of such compounds can be determined by standard pharmaceuticalprocedures in cell cultures or experimental animals, e.g., fordetermining the LD₅₀ (the dose lethal to 50% of the population) and theED₅₀ (the dose therapeutically effective in 50% of the population). Thedose ratio between toxic and therapeutic effects is the therapeuticindex, which is expressed as the ratio between LD₅₀ and ED₅₀. Compoundswhich exhibit high therapeutic indices are preferred. The data obtainedfrom such data can be used in formulating a dosage range for use inhumans. The dosage of such compounds preferably lies within a range ofcirculating concentrations that include the ED₅₀ with little or notoxicity. The dosage can vary within this range depending upon thedosage form employed, and the route of administration utilized.

The exact formulation, route of administration, and dosage can be chosenby the individual physician in view of the patient's condition. Dosageamount and interval can be adjusted individually to provide plasmalevels of the active moiety which are sufficient to maintain thetherapeutic effects.

As appreciated by persons skilled in the art, reference herein totreatment extends to prophylaxis, as well as to treatment of establisheddiseases or symptoms. It is further appreciated that the amount of acompound of the invention required for use in treatment varies with thenature of the condition being treated, and with the age and thecondition of the patient, and is ultimately determined by the attendantphysician or veterinarian. In general, however, doses employed for adulthuman treatment typically are in the range of 0.001 mg/kg to about 100mg/kg per day. The desired dose can be conveniently administered in asingle dose, or as multiple doses administered at appropriate intervals,for example as two, three, four or more subdoses per day. In practice,the physician determines the actual dosing regimen which is mostsuitable for an individual patient, and the dosage varies with the age,weight, and response of the particular patient. The above dosages areexemplary of the average case, but there can be individual instances inwhich higher or lower dosages are merited, and such are within the scopeof the present invention.

Formulations of the present invention can be administered in a standardmanner for the treatment of the indicated diseases, such as orally,parenterally, transmucosally (e.g., sublingually or via buccaladministration), topically, transdermally, rectally, via inhalation(e.g., nasal or deep lung inhalation). Parenteral administrationincludes, but is not limited to intravenous, intraarterial,intraperitoneal, subcutaneous, intramuscular, intrathecal, andintraarticular. Parenteral administration also can be accomplished usinga high pressure technique, like POWDERJECT™.

For buccal administration, the composition can be in the form of tabletsor lozenges formulated in conventional manner. For example, tablets andcapsules for oral administration can contain conventional excipientssuch as binding agents (for example, syrup, accacia, gelatin, sorbitol,tragacanth, mucilage of starch or polyvinylpyrrolidone), fillers (forexample, lactose, sugar, microcrystalline, cellulose, maize-starch,calcium phosphate or sorbitol), lubricants (for example, magnesium,stearate, stearic acid, talc, polyethylene glycol or silica),disintegrants (for example, potato starch or sodium starch glycollate),or wetting agents (for example, sodium lauryl sulfate). The tablets canbe coated according to methods well known in the art.

Alternatively, the compounds of the present invention can beincorporated into oral liquid preparations such as aqueous or oilysuspensions, solutions, emulsions, syrups, or elixirs, for example.Moreover, formulations containing these compounds can be presented as adry product for constitution with water or other suitable vehicle beforeuse. Such liquid preparations can contain conventional additives, suchas suspending agents, such as sorbitol syrup, methyl cellulose,glucose/sugar syrup, gelatin, hydroxyethylcellulose,hydroxypropylmethylcellulose, carboxymethyl cellulose, aluminum stearategel, and hydrogenated edible fats; emulsifying agents, such as lecithin,sorbitan monooleate, or acacia; nonaqueous vehicles (which can includeedible oils), such as almond oil, fractionated coconut oil, oily esters,propylene glycol, and ethyl alcohol; and preservatives, such as methylor propyl p-hydroxybenzoate and sorbic acid.

Such preparations also can be formulated as suppositories, e.g.,containing conventional suppository bases, such as cocoa butter or otherglycerides. Compositions for inhalation typically can be provided in theform of a solution, suspension, or emulsion that can be administered asa dry powder or in the form of an aerosol using a conventionalpropellant, such as dichlorodifluoromethane or trichlorofluoromethane.Typical topical and transdermal formulations comprise conventionalaqueous or nonaqueous vehicles, such as eye drops, creams, ointments,lotions, and pastes, or are in the form of a medicated plaster, patch,or membrane.

Additionally, compositions of the present invention can be formulatedfor parenteral administration by injection or continuous infusion.Formulations for injection can be in the form of suspensions, solutions,or emulsions in oily or aqueous vehicles, and can contain formulationagents, such as suspending, stabilizing, and/or dispersing agents.Alternatively, the active ingredient can be in powder form forconstitution with a suitable vehicle (e.g., sterile, pyrogen-free water)before use.

A composition in accordance with the present invention also can beformulated as a depot preparation. Such long acting formulations can beadministered by implantation (for example, subcutaneously orintramuscularly) or by intramuscular injection. Accordingly, thecompounds of the invention can be formulated with suitable polymeric orhydrophobic materials (e.g., an emulsion in an acceptable oil), ionexchange resins, or as sparingly soluble derivatives (e.g., a sparinglysoluble salt).

For veterinary use, a compound of formula (II), or nontoxic saltsthereof, is administered as a suitably acceptable formulation inaccordance with normal veterinary practice. The veterinarian can readilydetermine the dosing regimen and route of administration that is mostappropriate for a particular animal.

Thus, the invention provides in a further aspect a pharmaceuticalcomposition comprising a compound of the formula (II), together with apharmaceutically acceptable diluent or carrier therefor. There isfurther provided by the present invention a process of preparing apharmaceutical composition comprising a compound of formula (II), whichprocess comprises mixing a compound of formula (II), together with apharmaceutically acceptable diluent or carrier therefor.

Specific, nonlimiting examples of compounds of structural formula (II)are provided below, the synthesis of which were performed in accordancewith the procedures set forth below.

Generally, compounds of structural formula (II) can be preparedaccording to the following synthetic scheme. In the scheme describedbelow, it is understood in the art that protecting groups can beemployed where necessary in accordance with general principles ofsynthetic chemistry. These protecting groups are removed in the finalsteps of the synthesis under basic, acidic, or hydrogenolytic conditionswhich are readily apparent to those skilled in the art. By employingappropriate manipulation and protection of any chemical functionalities,synthesis of compounds of structural formula (II) not specifically setforth herein can be accomplished by methods analogous to the schemes setforth below.

Unless otherwise noted, all starting materials were obtained fromcommercial suppliers and used without further purification. Allreactions and chromatography fractions were analyzed by thin-layerchromatography on 250-mm silica gel plates, visualized with UV(ultraviolet) light or I₂ (iodine) stain. Products and intermediateswere purified by flash chromatography, or reverse-phase HPLC.

The compounds of general structural formula (II) can be prepared, forexample, as set forth in the following synthetic scheme. Other syntheticroutes also are known to persons skilled in the art. The followingreaction scheme provides a compound of structural formula (II), whereinR¹ and R², i.e., C₂H₅ and cyclopentyl, are determined by the startingmaterials. Proper selection of other starting materials, or performingconversion reactions on intermediates and examples, provide compounds ofgeneral structural formula (II) having other recited R¹ through R¹¹substituents.

The following illustrates the synthesis of various intermediates andcompounds of structural formula (II). The following examples areprovided for illustration and should not be construed as limiting.

EXAMPLE 1 Preparation of(S)-4-(3-Cyclopentyloxy-4-methoxyphenyl)-3-methyl-3-[1-(methylhydrazono)ethyl]-pyrrolidine-1-carboxylicacid methyl ester (1a) and(R)-4-(3-Cyclopentyloxy-4-methoxyphenyl)-3-methyl-3-[1-(methylhydrazono)ethyl]-pyrrolidine-1-carboxylicacid methyl ester (1b)

To a stirred solution of(R)-3-acetyl-4-(3-cyclopentyloxy-4-methoxyphenyl)-3-methyl-pyrrol-idine-1-carboxylicacid methyl ester (see Example 12 of Feldman et al. U.S. Pat. No.5,665,654, incorporated herein by reference) (or(R)-3-acetyl-4-(3-cyclopentyloxy-4-methoxyphenyl)-3-methyl-pyrroli-dine-1-carboxylicacid methyl ester) (0.133 mmol, 50 mg) in methanol (2 mL) with catalyticamount of acetic acid (20 μL) was added methyl hydrazine (0.147 mmol,7.8 μL). The reaction was heated gently for 36 hours, and three moreportions of methyl hydrazine were added. The resulting hydrazone waspurified by HPLC. The named product was confirmed by HNMR.

¹H NMR (300 MHz, CDCl₃) δ (ppm) 6.8 (d, 1H); 6.68 (m, 2H); 4.73 (bm,1H); 3.91-4.03 (m, 2H); 3.83 (s, 3H); 3.75 (s, 3H); 3.47-3.69 (m, 2H);2.98 (s, 3H); 1.83-1.92 (bm, 8H); 1.6 (bm, 2H); 1.0 (s, 3H).

EXAMPLE 2

To a solution of(3S,4R)-3-acetyl-4-(3-cyclopentyloxy-4-methoxyphenyl)-3-methyl-pyrrolidine-1-carboxylicacid methyl ester (50 mg, 0.133 mmol) in 0.5 mL ethanol was addedhydroxylamine hydrochloride (103 mg, 1.5 mmol) and 0.1 ml water. Thesuspension was heated to 50° C. and stirred overnight. The solution thenwas cooled to room temperature and concentrated under reduced pressure.Purification of HPLC on a C18 column (Luna 10 μ, C128, 250×10 mm) usinga gradient elution of 50-100% acetonitrile-water (0.05% TFA) gaveproduct 2(a) as a white powder upon lyophilization (24.4 mg, 47% yield).Example 2(b) was prepared by an identical procedure.

¹H NMR (300 MHz, CDCl₃) δ (ppm): 6.84-6.76 (m, 1H, aromatic); 6.70-6.59(m, 2H, aromatic); 4.87-4.57 (m, 1H); 3.96-3.60 (m, 3H); 3.83 (s, 3H,OCH₃); 3.75 (s, 3H, OCH₃); 3.59-3.45 (m, 1H); 3.40-3.21 (m, 1H); 1.92(s, 3H, CH₃); 1.90-1.48 (m, 8H, cyclopentyl); 0.96 (s, 3H, CH₃).

Intermediate 1

Preparation of 3-(Indan-2-yloxy)-4-methoxy-benzaldehyde

A solution of 3-hydroxy-4-methoxy-benzaldehyde (15.2 g, 100 mmol, 1 eq),2-indanol (12.1 g, 90 mmol, 0.9 eq), and triphenylphosphine (26.2 g, 100mmol, 1 eq) in dry THF (300 mL) was treated dropwise withdiisopropylazodicarboxylate (19.6 mL, 100 mmol, 1 eq). The reactionmixture was stirred at reflux for 16 hours, then cooled and diluted withdiethyl ether (500 mL). The solution was washed with water (2×150 mL), 1M NaOH (4×125 mL), and saturated NaCl (sodium chloride) (2×100 mL),dried with CH₂Cl₂, then concentrated to provide a syrup, whichsolidified upon standing. The solid was suspended in diethyl ether (350mL) and stirred overnight to break up all chunks. The solid wascollected by vacuum filtration and recrystallized from ethanol/water(21.4 g). The ethereal filtrate was concentrated and purified by flashchromatography (silica gel, 7.5×36 cm Biotage KP-Sil column, eluted with25% ethyl acetate in heptane) to yield an additional 5 g of product. ¹HNMR (300 MHz, CDCl₃) δ 9.86 (s, 1H), 7.49-7.44 (m, 2H), 7.25-7.16 (m,4H), 6.97 (d, J=8.7 Hz, 1H), 5.29-5.22 (m, 1H), 3.89 (s, 1H), 3.45 (dd,J=16.7, 6.6 Hz, 2H), 3.24 (dd, J=16.7, 3.6 Hz, 2H). ¹³C NMR (75 MHz,CDCl₃) δ 190.9, 155.5, 147.9, 140.4, 130.0, 126.9, 126.8, 124.7, 112.1,111.0, 78.9, 56.1, 39.7.

Intermediate 2(E)-4-[3-(Indan-2-yloxy)-4-methoxyphenyl]-3-methylbut-3-en-2-one

A solution of Intermediate 1 (0.14 mol, 1 eq) and 2-butanone (50 mL,0.56 mol, 4 eq) in dry THF (50 mL) was cooled to −4° C. Hydrogenchloride gas was passed through the well-stirred solution for severalminutes, and the reaction mixture was capped and stored at −4° C. for 16hours. The mixture was poured into a well stirred solution of ice-coldsaturated NaHCO₃ (about 2 L). If necessary, the pH was adjusted to >7with saturated NaHCO₃, and the mixture was extracted with ethyl acetate(3×300 mL). The ethyl acetate layer was washed with NaHCO₃ (2×200 mL),water (2×200 mL), and saturated NaCl (2×200 mL), dried with CH₂Cl₂, thenconcentrated to a syrup. The crude mixture was purified by flashchromatography (silica gel, 7.5×36 cm Biotage KP-Sil column, eluted with25% ethyl acetate in heptane, to yield a solid product.

¹H NMR (300 MHz, CDCl₃) δ 7.49-7.43 (m, 2H), 7.26-7.15 (m, 5H), 6.90 (d,J=8.2 Hz, 1H), 5.25-5.16 (M, 1H), 3.85 (s, 3H), 3.38 (dd, J=16.7, 6.5Hz, 2H), 3.25 (dd, J=16.7, 3.8 Hz, 2H), 2.45 (S, 3H), 2.10 (d, J=1.1Hz).

Intermediate 3

1-{(3SR,4RS)-1-Benzyl-4-[3-(indan-2-yloxy)-4-methoxyphenyl]-3-methyl-pyrrolidin-3-yl}-ethanone

A solution of Intermediate 2 (50.6 mmol, 1 eq) andN-methoxymethyl-N-benzyl-trimethysilylmethylamine (50.6 mmol, 1 eq) indichloromethane (85 mL) at 0° C. was treated dropwise with a solution oftrifluoroacetic acid (1 M in dichloromethane, 5 mL, 5.1 mmol, 0.1 eq).After stirring at the same temperature for 30 minutes, the reactionmixture was stirred at room temperature for 16 hours. The solution wastreated with additional N-methoxymethyl-N-benzyltrimethysilylmethylamine(25.3 mmol, 0.5 eq), stirred 1 hour at room temperature, and treated fora third time with N-methoxymethyl-N-benzyl-trimethysilylmethylamine(25.3 mmol, 0.5 eq). The reaction mixture was concentrated, and theresidue was dissolved in ethyl acetate (500 mL). This solution waswashed with 1 N HCl (2×60 mL with 10. mL saturation NaCl added), water(250 mL), 1 M NaOH (250 mL), water (250 mL), saturated NaCl (2×100 mL),dried with CH₂Cl₂, and concentrated in vacuo. The residue was purifiedby flash chromatography (silica gel, 7.5×36 cm Biotage KP-Sil column,eluted with 5-10% diethyl ether in dichloromethane) to yield theproduct.

¹H NMR (300 MHz, CDCl₃) δ 7.38-7.16 (m, 9H), 6.88 (br s, 1H), 6.78 (brs, 2H), 5.18-5.13 (m, 1H), 3.82-3.73 (m, 2H), 3.79 (s, 3H), 3.60 (d,J=13.0 Hz, 1H), 3.41-3.17 (m, 4H), 3.14 (d, J=9.7 Hz, 1H), 3.05 (t,J=8.3 Hz, 1H), 2.84 (t, J=8.3 Hz, 1H), 2.44 (d, J=9.7 Hz, 1H), 2.24 (s,3H), 0.86 (s, 3H).

Intermediate 4

trans-(±)-3-Acetyl-4-[3-(indan-2-yloxy)-4-methoxyphenyl]-3-methyl-pyrrolidine-1-carboxylicacid methyl ester

A solution of Intermediate 3 (40.5 mmol, 1 eq) in acetonitrile (150 mL)was treated with methyl chloroformate (15.6 mL, 202.5 mmol, 5 eq), andthe mixture was stirred at reflux 1 hour. The reaction mixture wasconcentrated, and the residue was purified by flash chromatography(silica gel, 7.5×36 cm Biotage KP-Sil column, eluted with 50-60% ethylacetate in heptane) to afford the product.

¹H NMR (300 MHz, CDCl₃) δ 7.24-7.16 (m, 4H), 6.82 (d, J=8.8 Hz, 1H),6.75-6.72 (m, 2H), 5.18-5.10 (m, 1H), 3.91 (t, J=11.2 Hz, 1H), 3.80 (s,3H), 3.77-3.65 (m, 3H), 3.74 (s, 3H), 3.42-3.16 (m, 5H), 2.17 (d, J=6.8Hz, 3H), 1.04 (s, 3H). ¹³C NMR (75 MHz, CDCl₃) δ 210.1/209.9, 155.3,149.4, 146.9/146.8, 140.5/140.4, 130.5/130.0, 126.7, 124.7, 121.3/121.1,116.1/115.8, 111.9, 79.2, 58.2/57.4, 55.9, 54.7/54.2, 52.6, 50.2/50.0,48.5/48.1, 39.7, 26.6/26.5, 17.8.

EXAMPLE 3

To a solution of Intermediate 4 (102.4 mg, 0.24 mmol) in 0.5 mL ethanolwas added hydroxylamine hydrochloride (83.8 mg, 1.2 mmol) and 0.1 mLwater. The suspension was heated to 50° C. and stirred overnight. Thesolution then was cooled to room temperature and concentrated underreduced pressure. Purification by HPLC on a C18 column (Luna 10 μ, C18,250×10 mm) using a gradient elution of 50-100% acetonitrile-water (0.05%TFA) gave solid product (60 mg, 57% yield).

¹H NMR (300 MHz, CDCl₃) δ (ppm) 7.26-7.16 (m, 4H, aromatic), 6.83-6.77(m, 1H, aromatic), 6.74-6.71 (m, 2H), 5.14-5.11 (m, 1H), 3.92-3.64 (m,3H), 3.80 (s, 3H, OCH₃), 3.74 (s, 3H, OCH₃), 3.58-3.48 (m, 1H) 3.38-3.16(m, 5H), 1.92 (s, 3H, CH₃), 0.96 (s, 3H, CH₃).

The compounds of structural formula (II) were tested for an ability toinhibit PDE4. The ability of a compound to inhibit PDE4 activity isrelated to the IC₅₀ value for the compound, i.e., the concentration ofinhibitor required for 50% inhibition of enzyme activity. The IC₅₀ valuefor compounds of structural formula (II) were determined usingrecombinant human PDE4.

The compounds of the present invention typically exhibit an IC₅₀ valueagainst recombinant human PDE4 of less than about 50 μM, and preferablyless than about 25 μM, and more preferably less than about 15 μm. Thecompounds of the present invention typically exhibit an IC₅₀ valueagainst recombinant human PDE4 of less than about 1 μM, and often lessthan about 0.05 μM. To achieve the full advantage of the presentinvention, a present PDE4 inhibitor has an IC₅₀ of about 1 nM to about15 μM.

The IC₅₀ values for the compounds were determined fromconcentration-response curves typically using concentrations rangingfrom 0.1 pM to 500 μM. Tests against other PDE enzymes using standardmethodology, as described in Loughney et al., J. Biol. Chem., 271, pp.796-806 (1996), also showed that compounds of the present invention arehighly selective for the cAMP-specific PDE4 enzyme.

The compounds of structural formula (II) also were tested for an abilityto reduce TNFα secretion in human peripheral blood lymphocytes. Theability to reduce TNFα secretion is related to the EC₅₀ values (i.e.,the effective concentration of the compound capable of inhibiting 50% ofthe total TNFα).

The compounds of the present invention typically exhibit an EC₅₀ valueof less than about 50 μM, and preferably less than about 25 μM, and morepreferably less than about 15 μM. The compounds of the present inventionpreferably exhibit a PBL/TNFα EC₅₀ value of less than about 1 μM, andoLten less than about 0.05 μM. To achieve the full advantages of thepresent invention, a present PDE4 inhibitor has an EC₅₀ value of about 1nM to about 500 nM.

The production of recombinant human PDEs and the IC₅₀ and EC₅₀determinations can be accomplished by well-known methods in the art.Exemplary methods are described as follows:

EXPRESSION OF HUMAN PDEs Expression in Baculovirus-Infected SpodopteraFugiperda (Sf9) Cells

Baculovirus transfer plasmids were constructed using either pBlueBacIII(Invitrogen) or pFastBac (BRL-Gibco). The structure of all plasmids wasverified by sequencing across the vector junctions and by fullysequencing all regions generated by PCR. Plasmid pBB-PDE1A3/6 containedthe complete open reading frame of PDE1A3 (Loughney et al., J. Biol.Chem., 271, pp. 796-806 (1996)) in pBlueBacIII. Plasmid Hcam3 aBBcontained the complete open reading frame of PDE1C3 (Loughney et al.(1996)) in pBlueBacIII. Plasmid pBB-PDE3 A contained the complete openreading frame of PDE3 A (Meacci et al., Proc. Natl. Acad. Sci., USA, 89,pp. 3721-3725 (1992)) in pBlueBacIII.

Recombinant virus stocks were produced using either the MaxBac system(Invitrogen) or the FastBac system (Gibco-BRL) according to themanufacturer's protocols. In both cases, expression of recombinant humanPDEs in the resultant viruses was driven off the viral polyhedronpromoter. When using the MaxBac® system, virus was plaque purified twicein order to insure that no wild type (occ+) virus contaminated thepreparation. Protein expression was carried out as follows. Sf9 cellswere grown at 27° C. in Grace's Insect culture medium (Gibco-BRL)supplemented with 10% fetal bovine serum, 0.33% TC yeastolate, 0.33%lactalbumin hydrolysate, 4.2 mM NaHCO₃, 10 μg/mL gentamycin, 100units/mL penicillin, and 100 μg/mL streptomycin. Exponentially growingcells were infected at a multiplicity of approximately 2 to 3 virusparticles per cell and incubated for 48 hours. Cells were collected bycentrifugation, washed with nonsupplemented Grace's medium, andquick-frozen for storage.

Expression in Saccharomyces Cerevisiae (Yeast)

Recombinant production of human PDE1B, PDE2, PDE4A, PDE4B, PDE4C, PDE4D,PDE5, and PDE7 was carried out similarly to that described in Example 7of U.S. Pat. No. 5,702,936, incorporated herein by reference, exceptthat the yeast transformation vector employed, which is derived from thebasic ADH2 plasmid described in Price et al., Methods in Enzymology,185, pp. 308-318 (1990), incorporated yeast ADH2 promoter and terminatorsequences and the Saccharomyces cerevisiae host was theproteasedeficient strain BJ2-54 deposited on Aug. 31, 1998 with theAmerican Type Culture Collection, Manassas, Va., under accession numberATCC 74465. Transformed host cells were grown in 2×SC-leu medium, pH6.2, with trace metals, and vitamins. After 24 hours, YEPmedium-containing glycerol was added to a final concentration of2×YET/3% glycerol. Approximately 24 hr later, cells were harvested,washed, and stored at −70° C.

HUMAN PHOSPHODIESTERASE PREPARATIONS

Phosphodiesterase Activity Determinations

Phosphodiesterase activity of the preparations was determined asfollows. PDE assays utilizing a charcoal separation technique wereperformed essentially as described in Loughney et al. (1996). In thisassay, PDE activity converts [32P]cAMP or [32P]cGMP to the corresponding[32P]5′-AMP or [32P]5′-GMP in proportion to the amount of PDE activitypresent. The [32P]5′-AMP or [32P]5′-GMP then was quantitativelyconverted to free [32P]phosphate and unlabeled adenosine or guanosine bythe action of snake venom 5′-nucleotidase. Hence, the amount of[32P]phosphate liberated is proportional to enzyme activity. The assaywas performed at 30° C. in a 100 μL reaction mixture containing (finalconcentrations) 40 mM Tris HCl (pH 8.0), 1 μM ZnSO₄, 5 mM MgCl₂, and 0.1mg/mL bovine serum albumin (BSA). Alternatively, in assays assessingPDEl-specific activity, incubation mixtures further incorporated the useof 0.1 mM CaCl₂ and 10 μg/mL calmodulin. PDE enzyme was present inquantities that yield <30% total hydrolysis of substrate (linear assayconditions). The assay was initiated by addition of substrate (1 mM[32P]cAMP or cGMP), and the mixture was incubated for 12 minutes.Seventy-five (75) μg of Crotalus atrox venom then was added, and theincubation was continued for 3 minutes (15 minutes total). The reactionwas stopped by addition of 200 μL of activated charcoal (25 mg/mLsuspension in 0.1 M NaH₂PO₄, pH 4). After centrifugation (750×g for 3minutes) to sediment the charcoal, a sample of the supernatant was takenfor radioactivity determination in a scintillation counter and the PDEactivity was calculated.

Inhibitor analyses were performed similarly to the method described inLoughney et al., J. Biol. Chem., 271, pp. 796-806 (1996), except bothcGMP and cAMP were used, and substrate concentrations were kept below 32nM, which is far below the Km of the tested PDEs.

HUMAM PDE4A, 4B, 4C, 4D PREPARATIONS

Preparation of PDE4A from S. Cerevisiae

Yeast cells (50 g of yeast strain YI26 harboring HDUN1.46) were thawedat room temperature by mixing with 50 mL of Lysis Buffer (50 mM MOPS pH7.5, 10 μM ZnSO₄, 2 mM MgCl₂, 14.2 mM 2-mercaptoethanol, 5 μg/mL each ofpepstatin, leupeptin, aprotinin, 20 μg/mL each of calpain inhibitors Iand II, and 2 mM benzamidine HCl). Cells were lysed in a French®pressure cell (SLM-Aminco®, Spectronic Instruments) at 10° C. Theextract was centrifuged in a Beckman JA-10 rotor at 9,000 rpm for 22minutes at 4° C. The supernatant was removed and centrifuged in aBeckman TI45 rotor at 36,000 rpm for 45 minutes at 4° C.

PDE4A was precipitated from the high-speed supernatant by the additionof solid ammonium sulfate (0.26 9/mL supernatant) while stirring in anice bath and maintaining the pH between 7.0 and 7.5. The precipitatedproteins containing PDE4A were collected via centrifugation in a BeckmanJA-10 rotor at 9,000 rpm for 22 minutes. The precipitate was resuspendedin 50 mL of Buffer G (50 mM MOPS pH 7.5, 10 μM ZnSO₄, 5 mM MgCl₂, 100 mMNaCl, 14.2 mM 2-mercaptoethanol, 2 mM benzamidine HCl, 5 μg/mL each ofleupeptin, pepstatin, and aprotinin, and 20 μg/mL each of calpaininhibitors I and II) and passed through a 0.45 μm filter.

The resuspended sample (50 to 100 mL) was loaded onto a 5×100 cm columnof Pharmacia SEPHACRYL® S-300 equilibrated in Buffer C. Enzyme activitywas eluted at a flow rate of 2 mL/min and pooled for laterfractionation.

The PDE4A isolated from gel filtration chromatography was applied to a1.6×20 cm column of Sigma Cibacron Blue Agarose-type 300 (10 mL)equilibrated in Buffer A (50 mM MOPS pH 7.5, 10 μM ZnSO₄, 5 MM MgCl₂,14.2 mM 2-mercaptoethanol, and 100 mM benzamidine HCl). The column waswashed in succession with 50 to 100 mL of Buffer A, 20 to 30 mL ofBuffer A containing 20 mM 5′-AMP, 50 to 100 mL of Buffer A containing1.5 M NaCl, and 10 to 20 mL of Buffer C (50 mM Tris HCl pH 8, 10 μMZnSO₄, 14.2 mM 2-mercaptoethanol, and 2 mM benzamidine HCl). The enzymewas eluted with 20 to 30 mL of Buffer C containing 20 mM cAMP.

The PD activity peak was pooled, and precipitated with ammonium sulfate(0.33 g/mL enzyme pool) to remove excess cyclic nucleotide. TheQrecipitated proteins were resuspended in Buffer X (25 mM MOPS pH 7.5, 5μM ZnSO₄, 50 mM NaCl, 1 mM DTT, and 1 mM benzamidine HCl), and desaltedvia gel filtration on a Pharmacia PD-10® column per manufacturer'sinstructions. The enzyme was quick-frozen in a dry ice/ethanol bath andstored at −70° C.

The resultant preparations were about >80% pure by SDS-PAGE. Thesepreparations had specific activities of about 10 to 40 μmol cAMPhydrolyzed per minute per milligram protein.

Preparation of PDE4B from S. Cerevisiae

Yeast cells (150 g of yeast strain YI23 harboring HDUN2.32) were thawedby mixing with 100 mL glass beads (0.5 mM, acid washed) and 150 mL LysisBuffer (50 mM MOPS pH 7.2, 2 mM EDTA, 2 mM EGTA, 1 mM DTT, 2 mMbenzamidine HCl, 5 μg/mL each of pepstatin, leupeptin, aprotinin,calpain inhibitors I and II) at room temperature. The mixture was cooledto 4° C., transferred to a Bead-Beater®, and the cells lysed by rapidmixing for 6 cycles of 30 seconds each. The homogenate was centrifugedfor 22 minutes in a Beckman J2-21 M centrifuge using a JA-10 rotor at9,000 rpm and 4° C. The supernatant was recovered and centrifuged in aBeckman XL-80 ultracentrifuge using a TI45 rotor at 36,000 rpm for 45minutes at 4° C. The supernatant was recovered and PDE4B wasprecipitated by the addition of solid ammonium sulfate (0.26 g/mLsupernatant) while stirring in an ice bath and maintaining the pHbetween 7.0 and 7.5. This mixture was then centrifuged for 22 minutes ina Beckman J2 centrifuge using a JA-10 rotor at 9,000 rpm (12,000×g). Thesupernatant was discarded and the pellet was dissolved in 200 mL ofBuffer A (50 mM MOPS pH 7.5, 5 mM MgCl₂, 1 mM DTT, 1 mM benzamidine HCl,and 5 μg/mL each of leupeptin, pepstatin, and aprotinin). The pH andconductivity were corrected to 7.5 and 15-20 mS, respectively.

The resuspended sample was loaded onto a 1.6×200 cm column (25 mL) ofSigma Cibacron Blue Agarose-type 300 equilibrated in Buffer A. Thesample was cycled through the column 4 to 6 times over the course of 12hours. The column was washed in succession with 125 to 250 mL of BufferA, 125 to 250 mL of Buffer A containing 1.5 M NaCl, and 25 to 50 mL ofBuffer A. The enzyme was eluted with 50 to 75 mL of Buffer E (50 mM TrisHCl pH 8, 2 mM EDTA, 2 mM EGTA, 1 mM DTT, 2 mM benzamidine HCl, and 20mM cAMP) and 50 to 75 mL of Buffer E containing 1 M NaCl. The PDEactivity peak was pooled, and precipitated with ammonium sulfate (0.4g/mL enzyme pool) to remove excess cyclic nucleotide. The precipitatedproteins were resuspended in Buffer X (25 mM MOPS pH 7.5, 5 μM ZnSO₄, 50mM NaCl, 1 mM DTT, and 1 mM benzamidine HCl) and desalted via gelfiltration on a Pharmacia PD-10® column per manufacturer's instructions.The enzyme pool was dialyzed overnight against Buffer X containing 50%glycerol. This enzyme was quick-frozen in a dry ice/ethanol bath andstored at −70° C.

The resultant preparations were about >90% pure by SDS-PAGE. Thesepreparations had specific activities of about 10 to 50 μmol cAMPhydrolyzed per minute per milligram protein.

Preparation of PDE4C from S. Cerevisiae

Yeast cells (150 g of yeast strain YI30 harboring HDUN3.48) were thawedby mixing with 100 mL glass beads (0.5 mM, acid washed) and 150 mL LysisBuffer (50 mM MOPS pH 7.2, 2 mM EDTA, 2 mM EGTA, 1 mM DTT, 2 mMbenzamidine HCl, 5 μg/mL each of pepstatin, leupeptin, aprotinin,calpain inhibitors I and II) at room temperature. The mixture was cooledto 4° C., transferred to a BEAD-BEATER®, and the cells lysed by rapidmixing for 6 cycles of 30 sec each. The homogenate was centrifuged for22 minutes in a Beckman J2-21 M centrifuge using a JA-10 rotor at 9,000rpm and 4° C. The supernatant was recovered and centrifuged in a BeckmanXL-80 ultracentrifuge using a TI45 rotor at 36,000 rpm for 45 minutes at4° C.

The supernatant was recovered and PDE4C was precipitated by the additionof solid ammonium sulfate (0.26 g/mL supernatant) while stirring in anice bath and maintaining the pH between 7.0 and 7.5. Thirty minuteslater, this mixture was centrifuged for 22 minutes in a Beckman J2centrifuge using a JA-10 rotor at 9,000 rpm (12,000×g). The supernatantwas discarded and the pellet was dissolved in 200 mL of Buffer A (50 mMMOPS pH 7.5, 5 mM MgCl₂, 1 mM DTT, 2 mM benzamidine HCl, and 5 μg/mLeach of leupeptin, pepstatin, and aprotinin). The pH and conductivitywere corrected to 7.5 and 15-20 mS, respectively.

The resuspended sample was loaded onto a 1.6×20 cm column (25 mL) ofSigma Cibacron Blue Agarose-type 300 equilibrated in Buffer A. Thesample was cycled through the column 4 to 6 times over the course of 12hours. The column was washed in succession with 125 to 250 mL of BufferA, 125 to 250 mL of Buffer A containing 1.5 M NaCl, and then 25 to 50 mLof Buffer A. The enzyme was eluted with 50 to 75 mL of Buffer E (50 mMTris HCl pH 8, 2 mM EDTA, 2 mM EGTA, 1 mM DTT, 2 mM benzamidine HCl, and20 mM cAMP) and 50 to 75 mL of Buffer E containing 1 M NaCl. The PDE4Cactivity peak was pooled, and precipitated with ammonium sulfate (0.4g/mL enzyme pool) to remove excess cyclic nucleotide. The precipitatedproteins were resuspended in Buffer X (25 mM MOPS pH 7.2, 5 μM ZnSO₄, 50mM NaCl, 1 mM DTT, and 1 mM benzamidine HCl) and desalted via gelfiltration on a Pharmacia PD-10®, column per manufacurer's instructions.The enzyme pool was dialyzed overnight against Buffer X containing 50%glycerol. This enzyme was quick-frozen in a dry ice/ethanol bath andstored at −70° C.

The resultant preparations were about >80% pure by SDS-PAGE. Thesepreparations had specific activities of about 10 to 20 μmol cAMPhydrolyzed per minute per milligram protein.

Preparation of PDE4 D from S. Cerevisiae

Yeast cells (100 g of yeast strain YI29 harboring HDUN4.11) were thawedby mixing with 150 mL glass beads (0.5 mM, acid washed) and 150 mL LysisBuffer (50 mM MOPS pH 7.2, 10 μM ZnSO₄, 2 mM MgCl₂, 14.2 mM2-mercaptoethanol, 2 mM benzamidine HCl, 5 μg/mL each of pepstatin,leupeptin, aprotinin, calpain inhibitors I and II) at room temperature.The mixture was cooled to 4° C., transferred to a Bead-Beater®, and thecells lysed by rapid mixing for 6 cycles of 30 sec each. The homogenatewas centrifuged for 22 minutes in a Beckman J2-21 M centrifuge using aJA-10 rotor at 9,000 rpm and 4° C. The supernatant was recovered andcentrifuged in a Beckman XL-80 ultracentrifuge using a TI45 rotor at36,000 rpm for 45 minutes at 4° C. The supernatant was recovered andPDE4 D was precipitated by the addition of solid ammonium sulfate (0.33g/mL supernatant) while stirring in an ice bath and maintaining the pHbetween 7.0 and 7.5. Thirty minutes later, this mixture was centrifugedfor 22 minutes in a Beckman J2 centrifuge using a JA-10 rotor at 9,000rpm (12,000×g). The supernatant was discarded and the pellet wasdissolved in 100 mL of Buffer A (50 mM MOPS pH 7.5, 10 μM ZnSO₄, 5 mMMgCl₂, 14.2 mM 2-mercaptoethanol, 100 mM benzamidine HCl, and 5 μg/mLeach of leupeptin, pepstatin, aprotinin, calpain inhibitor I and II).The pH and conductivity were corrected to 7.5 and 15-20 mS,respectively.

At a flow rate of 0.67 mL/min, the resuspended sample was loaded onto a1.6×20 cm column (10 mL) of Sigma Cibacron Blue Agarose-type 300equilibrated in Buffer A. The column was washed in succession with 50 to100 mL of Buffer A, 20 to 30 mL of Buffer A containing 20 mM 5′-AMP, 50to 100 mL of Buffer A containing 1.5 M NaCl, and then 10 to 20 mL ofBuffer C (50 mM Tris HCl pH 8, 10 μM ZnSO₄, 14.2 mM 2-mercaptoethanol, 2mM benzamidine HCl). The enzyme was eluted with 20 to 30 mL of Buffer Ccontaining 20 mM cAMP.

The PDE4 D activity peak was pooled and precipitated with ammoniumsulfate (0.4 g/mL enzyme pool) to remove excess cyclic nucleotide. Theprecipitated proteins were resuspended in Buffer X (25 mM MOPS pH 7.2, 5μM ZnSO₄, 50 mM NaCl, 1 mM DTT, and 1 mM benzamidine HCl) and desaltedvia gel filtration on a Pharmacia PD-10® column per manufacturer'sinstructions. The enzyme pool was dialyzed overnight against Buffer Xcontaining 50% glycerol. This enzyme preparation was quick-frozen in adry ice/ethanol bath and stored at −70° C.

The resultant preparations were about >80% pure by SDS-PAGE. Thesepreparations had specific activities of about 20 to 50 μmol cAMPhydrolyzed per minute per milligram protein.

Lipopolysaccharide-Stimulated TNFα Release from Human Peripheral BloodLymphocytes

To assess the ability of a compound to reduce TNFα secretion in humanperipheral blood lymphocytes (PBL), the following tests were performed.Previous studies have demonstrated that incubation of human PBL withcAMP-elevating agents, such as prostaglandin E21, forskolin,8-bromo-cAMP, or dibutryl-cAMP, inhibits the secretion of TNFα by thecells when stimulated by lipopolysaccharide (LPS; endotoxin).Accordingly, preliminary experiments have been performed to demonstratethat selective PDE4 inhibitors, such as rolipram, inhibit LPS-inducedTNFα secretion from human lymphocytes in a dose-dependent fashion.Hence, TNFα secretion from human PBL was used as a standard for theability of a compound to elevate intracellular cAMP concentrationsand/or to inhibit PDE4 activity within the cell.

Heparinized blood (approximately 30 mL) drawn from human volunteers wasmixed 1:1 with Dulbecco's modified phosphate-buffered saline. Thismixture was mixed 1:1 with HISTOPAQUE® and centrifuged at 1,500 rpm atroom temperature without braking in the swinging bucket of a Beckmanmodel TJ6 centrifuge. Erythrocytes were centrifuged to the bottom of thetubes, and serum remained at the surface of the tubes. A layercontaining lymphocytes sedimented between the serum and HISTOPAQUE®layers, and was removed by aspiration to a fresh tube. The cells werequantified and adjusted to 3×10⁶ cells/mL and a 100 μL aliquot is placedinto the wells of a 96 well plate. Test compounds and RPMI media(Gibco/BRL Life Sciences) are added to each of the wells 15 minutesprior to addition of bacterial LPS (25 mg/mL). The mixture was allowedto incubate for 20 hours at 37° C. in a humidified chamber. The cellsthen were separated by centrifuging at 800 rpm for 5 minutes at roomtemperature. An aliquot of 180 μL of supernatant was transferred to anew plate for determination of TNFα concentration. TNFα protein in thecell supernatant fluids was measured using a commercially availableenzyme-linked immunosorbent assay (ELISA) (CYTOSCREEN® Immunoassay Kitfrom Biosource International).

The cell-based assay provided the following results for variouspyrrolidine compounds of the present invention. The EC₅₀ values (i.e.,effective concentration of the compound capable of inhibiting 50% of thetotal TNFα) illustrate the ability of the present compounds to inhibitLPS-stimulated TNFα release from human PBL.

The table below illustrates the ability of compounds of formula (II) toinhibit PDE4 activity and TNFα release in vitro. In the following table,the IC₅₀ values were determined against human recombinant PDE4.

Example Number PDE4 IC₅₀ (M × 10⁻⁹) PBL/TNFα EC₅₀ (M × 10⁻⁹) 1a 115.976.0 1b 2.2 2.2 2a 49.0 281.0 2b 2.2 23.0 3  189.3 551.0

The data presented above shows that the present compounds are potentinhibitors of PDE4, e.g., the compounds have an IC₅₀ vs. humanrecombinant PDE4 of about 1 nM to about 15 μM. Preferred compounds havean IC₅₀ of about 50 nM or less, and especially preferred compounds havean IC₅₀ of about 25 nM or less.

Similarly, preferred compounds have a PBL/TNFα EC₅₀ about 1000 nM orless, and Preferably about 500 nM or less. More preferred compounds havea PBL/TNFα EC₅₀ of about 100 nM or less.

To achieve the full advantages of the present invention, the compoundhas an EC₅₀ vs. human recombinant PDE4 of about 50 nM or less and aPBL/TNFα EC₅₀ of about 1000 nM or less. More preferably, the compoundhas an IC₅₀ of about 25 nM or less and a PBL/TNFα EC₅₀ of about 500 nMor less.

ANIMAL MODELS

Combined Mouse endotoxin-stimulated TNFα Release and Locomotor ActivityAssay

The purpose of this study was to determine the efficacy of PDE4inhibitors in vivo in an LPS mouse model together with a determinationwith respect to central nervous system (CNS) side-effects manifested bya decrease in spontaneous mobility.

The test animals were female Balb/c mice, having an average weight ofabout 20 g. The PDE4 inhibitors, formulated in 30% Cremophor® EL, wereadministered via intraperitoneal (i.p.) injections at doses of 0.1, 1.0,10.0, and 100 mg/kg. Individual dose volumes (about 150 μL) wereadjusted based on the body weights measured. One hour later, 5 mg/kg LPSin a final volume of 200 μL was injected via the tail vein to eachanimal. Ninety minutes following the LPS treatment, the animals werebled and serum samples were collected before being stored at −70° C.until assayed.

For efficacy determination, the serum samples were diluted two-fold andTNFα levels were determined using the CYTOSCREEN® Immunoassay Kit(Biosource International). The data were averaged between triplicatesample subjects for each of the tested compounds.

Movement of the X-Y plane, or rearina up on the hind legs, wasquantified by counting the number of “light-beam” crosses per unit oftime. A decrease in the number of activity events is directlyproportional to the mobility or immobilization of the animal. Thequantitative scoring correlated well with the subjective measurementsdescribed above.

The following table summarizes the locomotor activity assay (mobility, %activity) results obtained by the above-described method:

Mobility (% activity at 50 mg/kg dose) or Example Number ED₅₀ (mg/kg) 1a64% activity 1b  6% activity 2a ED₅₀ ¹ (mg/kg) > 50 mg/kg 2b ED₅₀(mg/kg) = 7 mg/kg

effective dose, in mg/kg, that decreases spontaneous mobility 50% ofcontrol.

It also was determined that compounds of formula (II) have fewer centralnervous system side effects compared to rolipram and to compoundsdisclosed in Feldman et al. U.S. Pat. No. 5,665,754. It also was foundthat central nervous system activity is reiated to the absolutestereochemistry of the present compounds.

The results summarized above show that the compounds of the presentinvention are useful for selectively inhibiting PDE4 activity in amammal, without exhibiting the adverse CNS and emetic effects associatedwith prior PDE4 inhibitors.

Obviously, many modifications and variations of the invention ashereinbefore set forth can be made without departing from the spirit andscope thereof and, therefore, only such limitations should be imposed asare indicated by the appended claims.

What is claimed is:
 1. A method of inhibiting activation of humanT-lymphocytes in a mammal comprising administering to said mammal atherapeutically effective amount of a compound having a formula:

wherein Y is OR⁵ or NR⁵R⁶; R¹ is lower alkyl, bridged alkyl, aralkyl,cycloalkyl, a 5- or 6-membered saturated heterocycle,C₁₋₃alkylenecycloalkyl, aryl- or heteroaryl-substituted propargyl, aryl-or heteroaryl-substituted allyl, or halocycloalkyl; R² is hydrogen,methyl, or halo-substituted methyl; R³ is C(═O)OR⁷, C(═O)R⁷,C(═NH)NR⁸R⁹, C(═O)—NR⁸R⁹, aryl, or heteroaryl; R⁴ is hydrogen, loweralkyl, haloalkyl, cycloalkyl, or aryl; R⁵ and R⁶, independently, arehydrogen, lower alkyl, haloalkyl, cycloalkyl, aryl, heteroaryl, oralkaryl; R⁷ is branched or unbranched lower alkyl or aryl, and R⁷ can beoptionally substituted with one or more of OR⁸, NR⁸R⁹, or SR⁸; and R⁸and R⁹, same or different, are selected from the group consisting ofhydrogen, lower alkyl, cycloalkyl, aryl, heteroaryl, and aralkyl, or R⁸and R⁹ are taken together with the nitrogen to which they are attachedto form a 5-membered or 6-membered nonaromatic ring; R¹⁰ is hydrogen,alkyl, haloalkyl, cycloalkyl, aryl, C(═O)alkyl, C(═O)cycloalkyl,C(═O)aryl, CH₂OH, CH₂Oalkyl, CHO, CN, NO₂, or SO₂R¹¹; and R¹¹ is alkyl,cycloalkyl, trifluoromethyl, aryl, aralkyl, or NR⁸R⁹.
 2. The method ofclaim 1 wherein the compound has the structure:


3. The method of claim 1 wherein the compound has the structure:


4. A pharmaceutical composition comprising (a) a compound having aformula

wherein Y is OR⁵ or NR⁵R⁶; R¹ is lower alkyl, bridged alkyl, aralkyl,cycloalkyl, a 5- or 6-membered saturated heterocycle,C₁₋₃alkylenecycloalkyl, aryl- or heteroaryl-substituted propargyl, aryl-or heteroaryl-substituted allyl, or halocycloalkyl; R² is hydrogen,methyl, or halo-substituted methyl; R³ is C(═O)OR⁷, C(═O)R⁷,C(═NH)NR⁸R⁹, C(═O)—NR⁸R⁹, aryl, or heteroaryl; R⁴ is hydrogen, loweralkyl, haloalkyl, cycloalkyl, or aryl; R⁵ and R⁶, independently, arehydrogen, lower alkyl, haloalkyl, cycloalkyl, aryl, heteroaryl, oralkaryl; R⁷ is branched or unbranched lower alkyl or aryl, and R⁷ can beoptionally substituted with one or more of OR⁸, NR⁸R⁹, or SR⁸; and R⁸and R⁹, same or different, are selected from the group consisting ofhydrogen, lower alkyl, cycloalkyl, aryl, heteroaryl, and aralkyl, or R⁸and R⁹ are taken together with the nitrogen to which they are attachedto form a 5-membered or 6-membered nonaromatic ring; R¹⁰ is hydrogen,alkyl, haloalkyl, cycloalkyl, aryl, C(═O)alkyl, C(═O)cycloalkyl,C(═O)aryl, CH₂OH, CH₂Oalkyl, CHO, CN, NO₂, or SO₂R¹¹; and R¹¹ is alkyl,cycloalkyl, trifluoromethyl, aryl, aralkyl, or NR⁸R⁹; (b) apharmaceutically acceptable carrier, and (c) a second therapeutic agenthaving utility in the treatment of rheumatoid arthritis.